The GRE Calculator: Guest Post by Student Emmanuel Y.

As helpful as it might seem, the GRE calculator might have been responsible for a few lost points on Test Day. Let's look at an example:

Even if you know the formula for the sum of n terms in an arithmetic sequence (written in red below, but you DON'T need to memorize this for the GRE), attempting to plug 55, -47, and 4 into the formula and get the answer using the GRE calculator will NOT give you the correct answer.

Check it out:

gre calculator.jpg

The incorrect answer results because the GRE calculator -- a little calculator that pops up on the screen while you take the exam -- doesn't do PEMDAS for you.  (And no, you're not allowed to bring your own calculator.)

You could certainly still use the formula, and use the calculator more judiciously -- that is, plug individual calculations, like 2(-47), into the calculator, and then write that down on your paper, without trying to let the calculator do it all. 

Or, you could try this simpler solution that avoids the problem entirely.

Do you see the similarity between the first and the second method? 

The formula from the first method is just a compact way of writing the more logically intuitive method here: is the first term and a + (n + 1) d is the last term. Summing them up and dividing by two gives you the median. Multiplying the median by the number of terms gives you the sum terms of the sequence. 

Leaving aside the fancy sequence problem, though, know that plugging a long series of operations into the GRE calculator isn't a good idea.

Takeaways:

  • The GRE Calculator won't do PEMDAS for you.
  • Use the calculator for term-by-term calculations -- or, as in the example above, work from right to left. 
  • The sum of the first n terms of an arithmetic sequence is the median (which is found by adding the first and the last term and dividing by two) times the number of terms in the sequence. 

Thanks to Emmanuel for the guest post! Don't worry if that seemed a little advanced -- everything here is something you could learn in one class activity. Promise!